Pharmacologic characterization of botulinum toxin for basic science and medicine

Efficacy and Safety of Botulinum Toxin Type A in the Treatment of Trigeminal Neuralgia: An Update on Systematic Review With Meta-analyses

OBJECTIVE

Pain management in patients with TN is challenging, as facial pain often does not respond well to conventional therapies. Botulinum toxin type A (BTX-A) has been suggested as a potential treatment option, but there is limited evidence regarding its long-term efficacy. This review aimed to analyze the current data for the use of in the treatment of trigeminal neuralgia (TN) and highlight the evidence for its efficacy and safety.

METHODS

A comprehensive search was conducted in various databases (PubMed, Scopus, Embase, ClinicalTrials, and Cochrane Library) to identify clinical studies evaluating the use of BTX-A in TN until October 2023. Randomized controlled trials (RCTs), single-arm studies, and stratified studies were included in the analysis. The mean difference (MD), effect size (ES), and 95% confidence interval (CI) were estimated for visual analogue scale (VAS) scores, pain episode frequency, and the proportion of responders.

RESULTS

The analysis included 23 studies, including 4 RCTs, 14 single-arm studies, and 5 stratified studies. In the RCTs, BTX-A was found to significantly reduce mean VAS scores compared with baseline (ES: -4.05; 95% CI: -6.13, -1.97; P =0.002). In 19 non-RCTs, the pooled single-arm analysis revealed that BTX-A decreased VAS scores (ES: -5.19, 95% CI: -6.05, -4.33, P <0.001) and pain attack frequency (ES: -17.85, 95% CI: -23.36, -12.34, P <0.001) from baseline to the end of follow-up. The overall proportion of responders to BTX-A treatment was also significant (95% CI: 0.653, 0.761, P =0.003).

DISCUSSION

Current evidence indicates that BTX-A injection is an effective and safe option for patients with refractory TN or not responding to medical or surgical management. However, more high-quality studies are needed to further confirm its efficacy.

Is Botulinum Toxin Effective in Treating Orofacial Neuropathic Pain Disorders? A Systematic Review

BACKGROUND

The aim of this paper is to provide a systematic review of the literature regarding the clinical use of botulinum toxin (BTX) to treat various orofacial neuropathic pain disorders (NP).

METHODS

A comprehensive literature search was conducted using Medline, Web of Science, and the Cochrane Library databases. Only randomized clinical trials (RCT) published between 2003 and the end of June 2023, investigating the use of BTX to treat NP, were selected. PICO guidelines were used to select and tabulate the articles.

RESULTS

A total of 6 RCTs were selected. Five articles used BTX injections to treat classical trigeminal neuralgia, and one to treat post-herpetic neuralgia. A total of 795 patients received BTX injections. The selected studies utilised different doses and methods of injections and doses. All the selected studies concluded superiority of BTX injections over placebo for reducing pain levels, and 5 out 6 of them highlighted an improvement in the patient's quality of life. Most of the studies reported transient and mild side effects.

CONCLUSION

There is evidence of the efficacy of BTX injections in orofacial pain management. However, improved study protocols are required to provide direction for the clinical use of BTX to treat various orofacial neuropathic pain disorders.

Scientific review of the aesthetic uses of botulinum toxin type A

Botulinum toxin type A (BoNT-A), onabotulinumtoxinA (Botox) was approved by the United States Food and Drug Administration for temporary improvement of glabellar lines in patients 65 years and younger in 2002, and has also been used widely for aesthetic purposes such as hyperhidrosis, body shape contouring, and other noninvasive facial procedures. BoNT-A inhibits presynaptic exocytosis of acetylcholine (ACh)-containing vesicles into the neuromuscular junction at cholinergic nerve endings of the peripheral nervous system, thereby paralyzing skeletal muscles. ACh is the most broadly used neurotransmitter in the somatic nervous system, preganglionic and postganglionic fibers of parasympathetic nerves, and preganglionic fibers or postganglionic sudomotor nerves of sympathetic nerves. The scientific basis for using BoNT-A in various cosmetic procedures is that its function goes beyond the dual role of muscle paralysis and neuromodulation by inhibiting the secretion of ACh. Although the major target organs for aesthetic procedures are facial expression muscles, skeletal body muscles, salivary glands, and sweat glands, which are innervated by the somatic or autonomic nerves of the peripheral cholinergic nerve system, few studies have attempted to directly explain the anatomy of the areas targeted for injection by addressing the neural physiology and rationale for specific aesthetic applications of BoNT-A therapy. In this article, we classify the various cosmetic uses of BoNT-A according to the relevant component of the peripheral nervous system, and describe scientific theories regarding the anatomy and physiology of the cholinergic nervous system. We also review critical physiological factors and conditions influencing the efficacy of BoNT-A for the rational aesthetic use of BoNT-A. We hope that this comprehensive review helps promote management policies to support long-term, safe, successful practice. Furthermore, based on this, we look forward to developing and expanding new advanced indications for the aesthetic use of BoNT-A in the future.

The efficacy and safety of botulinum toxin type A in treatment of trigeminal neuralgia and peripheral neuropathic pain: A meta-analysis of randomized controlled trials

BACKGROUND

Although recent studies have shown that botulinum toxin-A (BTX-A) has a good analgesic effect on trigeminal neuralgia (TN) and peripheral neuropathic pain (PNP), the quality of evidence is low due to limited data. This meta-analysis is used to synthesize existing evidence for the treatment of these conditions with BTX-A.

METHODS

Relevant trials were accessed by using an electronic search in databases (Web of Science, PubMed, EMBASE, Cochrane Library, and ClinicalTrials.gov). Data from included randomized controlled trials (RCTs) on the efficacy and safety of BTX-A in treating TN and PNP were extracted for meta-analysis.

RESULTS

Finally, 10 RCTs (n = 391) were included in this meta-analysis. The pooled effect of BTX-A was superior to placebo based on pain intensity (SMD = -0.48, 95% CI [-0.74, 0.23] at 1 month, SMD = -0.58, 95% CI [-0.91, -0.24] at 2 months, and SMD = -0.55, 95% CI [-0.87, -0.22] at 3 months). Number needed to treat (NNT) for 50% pain intensity reduction showed better effect of BTX-A on TN and postherpetic neuralgia (PN). Adverse events associated with BTX-A were similar to placebo (OR = 1.58, 95% CI [0.51, 4.87], p = .424).

CONCLUSION

Pooled data from our meta-analysis suggest that BTX-A is efficacious and safe in treating TN and PNP. However, due to the limited sample size and heterogeneity, further larger and well-designed RCTs are imperative to validate these findings.

Factors affecting the therapeutic effect of botulinum toxin A on trigeminal neuralgia: A follow-up retrospective study of 152 patients

Botulinum toxin A (BTX-A) is a promising therapeutic modality against trigeminal neuralgia (TN) with certain controversies pertaining to its application. To provide further information on factors influencing the treatment outcomes of BTX-A, a retrospective study with 152 patients with TN treated with BTX-A was performed. The starting time and duration of the therapeutic effect, as well as side effects, of BTX-A in the treatment of TN were analyzed by sex, age, course of disease, number of branches and injected dose. A total of 136 patients exhibited symptom improvement within 2 weeks following BTX-A treatment as evaluated using a visual analog scale (VAS). The effect of BTX-A was sustained throughout the initial 6 months of the follow-up and was demonstrated to persist for as long as 28 months. Female sex, short disease course and high injection dose (>70 units) were associated with lower long-term VAS scores. Patients receiving short-term medium-(50–70 units) or high-dose injections were more likely to be completely cured. Patients with a median disease course (1–10 years) or multiple branches were more likely to exhibit facial asymmetry. Based on the stratified analysis, female patients with a median disease course (1–10 years) exhibited a higher incidence of side effects and male patients achieved better treatment outcomes with high BTX-A doses. BTX-A effectively alleviated patients with TN in both short or long term, although the treatment efficacy may depend on patient characteristics.

Progress in Applying the Three Rs to the Potency Testing of Botulinum Toxin Type A

Botulinum toxin type A (BTA) is being increasingly used for a range of therapeutic purposes and also for cosmetic reasons. For many years, the potency of BTA has been measured by using an LD50 assay in mice. This assay is a cause for concern due to its unpleasant nature and extreme severity, and the requirement for high numbers of mice to be used. Alternatives to this potency assay are presently reviewed with particular reference to the work at the National Institute for Biological Standards and Control (NIBSC), and to recent work by the UK manufacturer of the substance. An in vivo local paralysis assay with considerably less severity has been developed and is in use at the NIBSC. Alternative, ex vivo functional assays in use include the measurement of BTA-induced paralysis of neurally-stimulated rodent diaphragm or rat intercostal muscle. The latter method has the advantage of allowing more preparations to be derived from one animal. However, these ex vivo methods have not yet been fully validated and accepted by regulatory agencies as potency assays. Endopeptidase assays, although not measuring muscle paralysis directly, may provide a very useful consistency test for batch release and may replace the routine use of the LD50 test for that purpose. These assays measure the cleavage of the SNAP-25 protein (the final stage of BTA action), and have been validated for batch release by the National Control Laboratory (NIBSC), and are in regular use there. ELISA assays, used alongside the endopeptidase assay, also provide useful confirmatory information on the amounts of functional (and non-functional) BTA present. The UK manufacturer is further validating its endopeptidase assay, an ex vivo muscle assay and an ELISA. It is anticipated that their work will lead to a change in the product license, hopefully within the next two years, and will form a critical milestone towards the end of the LD50 potency test.

Safety, efficacy, and onset of a novel botulinum toxin type A (Nabota) for the treatment of glabellar frown lines: a single-arm, prospective, phase 4 clinical study

Background

Safety, efficacy, and time to onset of effect of botulinum toxin type A is of importance to persons who seek improvement in glabellar frown lines, but this has not been well studied. The aim of this study was to determine the safety, efficacy, and onset of action of a newly developed botulinum toxin type A (Nabota) for the treatment of glabellar frown lines.

Methods

This was a single-arm, open-label, and phase 4 clinical study. Forty-two subjects with glabellar lines were treated with five times of intramuscular injection of 0.1 mL (4 U/0.1 mL) for a total of 20 U of Nabota. Efficacy and safety were assessed at 2, 3, 4, 5, and 14 days. Efficacy was assessed by the investigator and it was defined as a 1-point change on a 4-point scale.

Results

Improvement in glabellar frown lines at maximum frown was observed in 85.4% of subjects 2 days after administration. Improvement in glabellar lines at rest was observed in 51.2% of subjects 2 days after administration, and the proportion of subjects showing improvement increased with time. No severe adverse events were recorded.

Conclusion

Onset of action was observed in the majority of subjects by 2 days after administration of Nabota. In addition, Nabota was found to be safe and effective for the treatment of glabellar frown lines.

Repeated Intrastriatal Botulinum Neurotoxin-A Injection in Hemiparkinsonian Rats Increased the Beneficial Effect on Rotational Behavior

Injection of botulinum neurotoxin-A (BoNT-A) into the striatum of hemiparkinsonian (hemi-PD) rats reduced apomorphine-induced rotation behavior significantly, for at least 3 months. Thereafter, rotation behavior increased again. We injected hemi-PD rats with 1 ng BoNT-A twice, the second injection following 6 months after the first one and tested the rats for apomorphine-induced rotations and spontaneous motor behaviors, i.e., corridor task and stepping test. To test the hypothesis that BoNT-A reduced striatal hypercholinism in hemi-PD rats, the acetylcholinesterase inhibitor donepezil was injected prior to separate apomorphine-induced rotation tests. In hemi-PD rats, the first BoNT-A injection led to a clear reduction of the apomorphine-induced rotations, and the second BoNT-A injection to a more massive and prolonged reaction. In hemi-PD rats whose apomorphine-induced rotation behavior was strongly reduced by an intrastriatal BoNT-A, subsequent donepezil injections led to significant increases of the rotation rate. Concerning corridor task and stepping test, neither first nor second BoNT-A injections changed hemi-PD rats' behavior significantly. The data give evidence for the possibility of repeated intrastriatal administrations of BoNT-A, for treatment of motor symptoms in experimental hemi-PD over a longer time.

Unilateral Botulinum Neurotoxin-A Injection into the Striatum of C57BL/6 Mice Leads to a Different Motor Behavior Compared with Rats

Different morphological changes in the caudate-putamen (CPu) of naïve rats and mice were observed after intrastriatal botulinum neurotoxin-A (BoNT-A) injection. For this purpose we here studied various motor behaviors in mice (n = 46) longitudinally up to 9 months after intrastriatal BoNT-A administration as previously reported for rats, and compared both outcomes. Apomorphine- and amphetamine-induced rotational behavior, spontaneous motor behavior, as well as lateralized neglect were studied in mice after the injection of single doses of BoNT-A into the right CPu, comparing them with sham-injected animals. Unilateral intrastriatal injection of BoNT-A in mice induced significantly increased contralateral apomorphine-induced rotations for 1 to 3 months, as well as significantly increased contralateral amphetamine-induced rotations 1 to 9 months after injection. In rats (n = 28), unilateral BoNT-A injection also induced significantly increased contralateral apomorphine-induced rotations 3 months after injection, but did not provoke amphetamine-induced rotations at all. Lateralized sensorimotor integration, forelimb preference, and forelimb stepping were significantly impaired on the left side. The differences in motor behaviors between rats and mice may be caused by different BoNT-A effects on cholinergic and catecholaminergic fibers in rat and mouse striata, interspecies differences in striatal receptor densities, and different connectomes of the basal ganglia.

Therapeutic efficacy and safety of Botulinum Toxin A Therapy in Trigeminal Neuralgia: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Several different interventions have been examined to alleviate pain and reduce frequency of trigeminal neuralgia (TN) paroxysms. However, some patients continue to have persistent or recurrent painful attacks. Using a systematic review and meta-analysis approach, we aimed to synthesize evidence from published randomized controlled trials (RCTs) regarding safety and efficacy of botulinum toxin type A (BTX-A) as a possible emerging choice of treatment for TN.

METHODS

We conducted an electronic search in 10 databases/electronic search engines to access relevant publications. All articles in all languages reporting RCTs on the efficacy and safety of BTX-A in the treatment of TN were included for systematic review and meta-analysis.

RESULTS

A total of four RCTs (n = 178) were identified for final meta-analysis. The overall effect favored BTX-A versus placebo in terms of proportion of responders (risk ratio RR = 2.87, 95 % confidence interval CI [1.76, 4.69], p <0.0001) with no significant detected heterogeneity (p = 0.31; I(2) = 4 %). Paroxysms frequency per day was significantly lower for BTX-A group (mean difference MD = -29.79, 95 % CI [-38.50,-21.08], p <0.00001) with no significant heterogeneity (p = 0.21; I(2) = 36 %).

CONCLUSION

Despite limited data, our results suggest that BTX-A may be an effective and safe treatment option for patients with TN. Further larger and well-designed RCTs are encouraged to translate these findings into better clinical outcome and better quality of life for TN patients.

Comparative characterization of botulinum neurotoxin subtypes F1 and F7 featuring differential substrate recognition and cleavage mechanisms

BoNT/F7, one of the seven subtypes of botulinum neurotoxin type F (F1 to F7), is the second-most divergent subtype of this group. Despite sharing >60% identity with BoNT/F1 at both holotoxin and enzymatic domain levels, it requires an N-terminal extended peptide substrate for efficient substrate cleavage, suggesting its unique substrate recognition and specificity mechanism. Substrate mapping and saturation mutagenesis analysis revealed that VAMP2 (20-65) was likely a minimally effective substrate for LC/F7 (light chain of BoNT/F7), and in addition, LC/F7 recognized VAMP2 in a unique way, which differed significantly from that of LC/F1, although both of them share similar substrate binding and hydrolysis mode. LC/F7 utilizes distinct pockets for specific substrate binding and recognition in particular for the B1, B2 and S2 sites recognitions. Our findings provide insights into the distinct substrate recognition features of BoNT subtypes and useful information for therapy development for BoNT/F.

Botulinum toxin suppression of CNS network activity in vitro

The botulinum toxins are potent agents which disrupt synaptic transmission. While the standard method for BoNT detection and quantification is based on the mouse lethality assay, we have examined whether alterations in cultured neuronal network activity can be used to detect the functional effects of BoNT. Murine spinal cord and frontal cortex networks cultured on substrate integrated microelectrode arrays allowed monitoring of spontaneous spike and burst activity with exposure to BoNT serotype A (BoNT-A). Exposure to BoNT-A inhibited spike activity in cultured neuronal networks where, after a delay due to toxin internalization, the rate of activity loss depended on toxin concentration. Over a 30 hr exposure to BoNT-A, the minimum concentration detected was 2 ng/mL, a level consistent with mouse lethality studies. A small proportion of spinal cord networks, but not frontal cortex networks, showed a transient increase in spike and burst activity with exposure to BoNT-A, an effect likely due to preferential inhibition of inhibitory synapses expressed in this tissue. Lastly, prior exposure to human-derived antisera containing neutralizing antibodies prevented BoNT-A induced inhibition of network spike activity. These observations suggest that the extracellular recording from cultured neuronal networks can be used to detect and quantify functional BoNT effects.

Overview of botulinum toxin as a treatment for spasticity in stroke patients

Spasticity after the occurrence of stroke induces limb deformity, functional disability and/or pain in patients, which limits their activities of daily living and deteriorates their quality of life. Botulinum toxin (BTX) has recently been reported as an efficacious therapeutic agent for the treatment of spasticity. Systematic review and meta-analysis studies have demonstrated that BTX therapy after stroke reduces spasticity and increases physical activity capacity and performance levels. Moreover, BTX can be used as an adjuvant in physiotherapy. Several studies have confirmed that the combination of BTX therapy and physiotherapy improves motor recovery. However, to date, only a few such combination studies have been conducted and their findings are considered preliminary and controversial. Therefore, future studies are required to determine the appropriate combination of treatment methods that will aid motor recovery.

Therapeutic efficacy and safety of botulinum toxin type A in trigeminal neuralgia: a systematic review

Trigeminal neuralgia is a common disorder caused mainly by compression of the trigeminal nerve root by an overlying blood vessel. Pharmacotherapy and surgery are ineffective or unsuitable in many patients. Therefore, other therapeutic modalities have been tried, including injection of botulinum toxin type A (BTX-A). This study aims to systematically review the therapeutic efficacy and safety of BTX-A in trigeminal neuralgia. PubMed, EMBASE, Cochrane Library Clinical Trials and Web of Science from January 1966 to March 2013 were searched with the terms of “botulinum toxin” AND “trigeminal neuralgia”, and references of related articles were traced. Data on the efficacy and safety of BTX-A in this disorder were extracted and analyzed by at least 2 reviewers. Data for individual studies were reported, and pooled data were analyzed if appropriate. Five prospective studies and one double-blind, randomized, placebo-controlled study were identified. Response was achieved in approximately 70-100% of patients, and the mean pain intensity and frequency were reduced by approximately 60-100% at 4 weeks after treatment in most studies. Major adverse events were not reported. Available studies show BTX-A may be effective in treatment of trigeminal neuralgia. However, well-designed randomized, controlled, double-blinded trial is still lacking. Future BTX-A treatment studies on optimal dose, duration of the therapeutic efficacy, common AEs, and the time and indications for repeat injection would be promising.

Unique substrate recognition mechanism of the botulinum neurotoxin D light chain

Botulinum neurotoxins are the most potent protein toxins in nature. Despite the potential to block neurotransmitter release at the neuromuscular junction and cause human botulism, they are widely used in protein therapies. Among the seven botulinum neurotoxin serotypes, mechanisms of substrate recognition and specificity are known to a certain extent in the A, B, E, and F light chains, but not in the D light chain (LC/D). In this study, we addressed the unique substrate recognition mechanism of LC/D and showed that this serotype underwent hydrophobic interactions with VAMP-2 at its V1 motif. The LC/D B3, B4, and B5 binding sites specifically recognize the hydrophobic residues in the V1 motif of VAMP-2. Interestingly, we identified a novel dual recognition mechanism employed by LC/D in recognition of VAMP-2 sites at both the active site and distal binding sites, in which one site of VAMP-2 was recognized by two independent, but functionally similar LC/D sites that were complementary to each other. The dual recognition strategy increases the tolerance of LC/D to mutations and renders it a good candidate for engineering to improve its therapeutic properties. In conclusion, in this study, we identified a unique multistep substrate recognition mechanism by LC/D and provide insights for LC/D engineering and antitoxin development.

Comparison of Fluorigenic Peptide Substrates PL50, SNAPtide, and BoTest A/E for BoNT/A Detection and Quantification

Detection and quantification of low doses of botulinum toxin serotype A (BoNT/A) in medicinal preparations require precise and sensitive methods. With mounting pressure from governmental authorities to replace the mouse LD50 assay, interest in alternative methods such as the endopeptidase assay, quantifying the toxin active moiety, is growing. Using internal collision-induced fluorescence quenching, Pharmaleads produced peptides encompassing the SNAP-25 cleavage site: a 17-mer (PL63) and a 48-mer (PL50) reaching the previously identified α-exosite, with PL50 showing higher apparent affinity for BoNT/A. Peptide mapping experiments revealed that this increased affinity is mainly due to a connecting peptide sequence between the N-terminus of PL63 and the α-exosite, identifying a new cooperative exosite on BoNT/A. Other endopeptidase substrates available, including SNAPTide and BoTest A/E, are both based on fluorescent resonance energy transfer (FRET) technology. To compare these assays, their limits of detection and quantification were determined using light chain or 150-kDa BoNT/A. Detection limits of PL50 and BoTest were over 100 times better than those using SNAPtide in standard conditions. Although the BoTest possessed a detection limit around 0.2 pM for either BoNT/A form, its quantification limit (9.7 pM) using purified BoNT/A was 12 times inferior to PL50, estimated at 0.8 pM, suitable for medicinal preparation quantification.

Insights into the mechanism of onabotulinumtoxinA in chronic migraine

OnabotulinumtoxinA has recently been approved by regulatory agencies in the UK and United States for treatment of chronic migraine based on data generated from the PREEMPT studies. As such, onabotulinumtoxinA is the only prophylactic therapy specifically approved for chronic migraine. Most headache clinicians would agree that acute episodic migraine and chronic migraine differ in their pathophysiology, etiology, diagnosis, and response to pharmacological as well as nonpharmacological therapies. Of the 7 botulinum neurotoxin serotypes, botulinum neurotoxin type A (onabotulinumtoxinA) has been the most thoroughly investigated in preclinical and clinical studies. Based on preclinical studies, onabotulinumtoxinA is known to inhibit the release of excitatory neurotransmitters from both motor and sensory neurons by preventing vesicle fusion to the cell membrane. In addition to the well-documented myorelaxant effects of this neurotoxin, onabotulinumtoxinA can exert a direct analgesic effect that likely involves inhibition of primary and secondary nociceptive neurons. The inhibitory effects of onabotulinumtoxinA are also likely to involve suppressing the activity of myogenic trigger points and decreasing the persistent nociceptive barrage that promotes and maintains central sensitization. This article describes possible mechanisms to explain how onabotulinumtoxinA functions as a therapy for chronic migraine and considers why treatment with the neurotoxin is not effective in some chronic migraineurs.

PEG precipitation coupled with chromatography is a new and sufficient method for the purification of botulinum neurotoxin type B [corrected]

Clostridium botulinum neurotoxins are used to treat a variety of neuro-muscular disorders, as well as in cosmetology. The increased demand requires efficient methods for the production and purification of these toxins. In this study, a new purification process was developed for purifying type B neurotoxin. The kinetics of C.botulinum strain growth and neurotoxin production were determined for maximum yield of toxin. The neurotoxin was purified by polyethylene glycol (PEG) precipitation and chromatography. Based on design of full factorial experiment, 20% (w/v) PEG-6000, 4 °C, pH 5.0 and 0.3 M NaCl were optimal conditions to obtain a high recovery rate of 87% for the type B neurotoxin complex, as indicated by a purification factor of 61.5 fold. Furthermore, residual bacterial cells, impurity proteins and some nucleic acids were removed by PEG precipitation. The following purification of neurotoxin was accomplished by two chromatography techniques using Sephacryl™ S-100 and phenyl HP columns. The neurotoxin was recovered with an overall yield of 21.5% and the purification factor increased to 216.7 fold. In addition, a mouse bioassay determined the purified neurotoxin complex possessed a specific toxicity (LD(50)) of 4.095 ng/kg.

Molecular mechanisms of substrate recognition and specificity of botulinum neurotoxin serotype F

BoNTs (botulinum neurotoxins) are both deadly neurotoxins and natural toxins that are widely used in protein therapies to treat numerous neurological disorders of dystonia and spinal spasticity. Understanding the mechanism of action and substrate specificity of BoNTs is a prerequisite to develop antitoxin and novel BoNT-derived protein therapy. To date, there is a lack of detailed information with regard to how BoNTs recognize and hydrolyse the substrate VAMP-2 (vesicle-associated membrane protein 2), even though it is known to be cleaved by four of the seven BoNT serotypes, B, D, F, G and TeNT (tetanus neurotoxin). In the present study we dissected the molecular mechanisms of VAMP-2 recognition by BoNT serotype F for the first time. The initial substrate recognition was mediated through sequential binding of VAMP-2 to the B1, B2 and B3 pockets in LC/F (light chain of BoNT serotype F), which directed VAMP-2 to the active site of LC/F and stabilized the active site substrate recognition, where the P2, P1' and P2' sites of VAMP-2 were specifically recognized by the S2, S1' and S2' pockets of LC/F to promote substrate hydrolysis. The understanding of the molecular mechanisms of LC/F substrate recognition provides insights into the development of antitoxins and engineering novel BoNTs to optimize current therapy and extend therapeutic interventions.

Intrastriatal botulinum toxin abolishes pathologic rotational behaviour and induces axonal varicosities in the 6-OHDA rat model of Parkinson's disease

Central pathophysiological pathways of basal ganglia dysfunction imply a disturbed interaction of dopaminergic and cholinergic circuits. In Parkinson's disease (PD) imbalanced cholinergic hyperactivity prevails in the striatum. Interruption of acetylcholine (ACh) release in the striatum by locally injected botulinum neurotoxin A (BoNT-A) has been studied in the rat 6-hydroxydopamine (6-OHDA) model of PD (hemi-PD). The hemi-PD was induced by injection of 6-OHDA into the right medial forebrain bundle. Motor dysfunction provoked by apomorphine-induced contralateral rotation was completely reversed for more than 3 months by ipsilateral intrastriatal application of 1-2 ng BoNT-A. Interestingly, BoNT-A injected alone into the right striatum of naïve rats caused a slight transient ipsilateral apomorphine-induced rotation, which lasted only for about one month. Immunohistochemically, large axonal swellings appeared within the striatum injected with BoNT-A, which we tentatively named BoNT-A-induced varicosities. They contained either choline acetyltransferase or tyrosine hydroxylase. These findings suggest a selective inhibition of evoked release of ACh by locally applied BoNT-A. Intrastriatal application of BoNT-A may antagonize localized relative functional disinhibited hypercholinergic activity in neurodegenerative diseases such as PD avoiding side effects of systemic anti-cholinergic treatment.

Botulinum neurotoxin type A (BoNTA) decreases the mechanical sensitivity of nociceptors and inhibits neurogenic vasodilation in a craniofacial muscle targeted for migraine prophylaxis

The mechanism by which intramuscular injection of BoNTA into the craniofacial muscles decreases migraine headaches is not known. In a blinded study, the effect of BoNTA on the mechanical and chemical responsiveness of individual temporalis muscle nociceptors and muscle neurogenic vasodilation was investigated in female rats. Mechanical threshold was measured for 3h following intramuscular injection of BoNTA or vehicle, and for 10 min after a subsequent injection of the algogen glutamate. Injection of BoNTA significantly increased the mechanical threshold of muscle nociceptors without altering the muscle surface temperature and blocked glutamate-induced mechanical sensitization and neurogenic vasodilation. None of these effects were reproduced by pancuronium-induced muscle paralysis. Western blot analysis of temporalis muscles indicated that BoNTA significantly decreased SNAP-25. Measurement of interstitial glutamate concentration with a glutamate biosensor indicated that BoNTA significantly reduced glutamate concentrations. The mechanical sensitivity of muscle nociceptors is modulated by glutamate concentration through activation of peripheral NMDA receptors. Immunohistochemical experiments were conducted and they indicated that half of the NMDA-expressing temporalis nerve fibers co-expressed substance P or CGRP. Additional electrophysiology experiments examined the effect of antagonists for NMDA, CGRP and NK1 receptors on glutamate-induced effects. Glutamate-induced mechanical sensitization was only blocked by the NMDA receptor antagonist, but muscle neurogenic vasodilation was attenuated by NMDA or CGRP receptor antagonists. These data suggest that injection of BoNTA into craniofacial muscles acts to decrease migraine headaches by rapidly decreasing the mechanical sensitivity of temporalis muscle nociceptors through inhibition of glutamate release and by attenuating the provoked release of CGRP from muscle nociceptors.

High-molecular weight protein toxins of marine invertebrates and their elaborate modes of action

High-molecular weight protein toxins significantly contribute to envenomations by certain marine invertebrates, e.g., jellyfish and fire corals. Toxic proteins frequently evolved from enzymes meant to be employed primarily for digestive purposes. The cellular intermediates produced by such enzymatic activity, e.g., reactive oxygen species or lysophospholipids, rapidly and effectively mediate cell death by disrupting cellular integrity. Membrane integrity may also be disrupted by pore-forming toxins that do not exert inherent enzymatic activity. When targeted to specific pharmacologically relevant sites in tissues or cells of the natural enemy or prey, toxic enzymes or pore-forming toxins even may provoke fast and severe systemic reactions. Since toxin-encoding genes constitute "hot spots" of molecular evolution, continuous variation and acquirement of new pharmacological properties are guaranteed. This also makes individual properties and specificities of complex proteinaceous venoms highly diverse and inconstant. In the present chapter we portray high-molecular weight constituents of venoms present in box jellyfish, sea anemones, sea hares, fire corals and the crown-of-thorns starfish. The focus lies on the latest achievements in the attempt to elucidate their molecular modes of action.

Detection and quantification of botulinum neurotoxin type a by a novel rapid in vitro fluorimetric assay

Botulinum neurotoxin type A (BoNT/A), the most poisonous substance known to humans, is a potential bioterrorism agent. The light-chain protein induces a flaccid paralysis through cleavage of the 25-kDa synaptosome-associated protein (SNAP-25), involved in acetylcholine release at the neuromuscular junction. BoNT/A is widely used as a therapeutic agent and to reduce wrinkles. The toxin is used at very low doses, which have to be accurately quantified. With this aim, internally quenched fluorescent substrates containing the fluorophore/repressor pair pyrenylalanine (Pya)/4-nitrophenylalanine (Nop) were developed. Nop and Pya were, respectively, introduced at positions 197 and 200 of the cleavable fragment (amino acids 187 to 203) of SNAP-25 (with norleucine at position 202 [Nle(202)]), which is acetylated at its N terminus and amidated at its C terminus. Cleavage of this peptide occurred between positions 197 and 198, as in SNAP-25, and was easily quantified by the strong fluorescence emission of the metabolite. To increase the assay sensitivity, the peptide sequence of the previous substrate was lengthened to account for exosite binding to BoNT/A. We synthesized the peptide PL50 (SNAP-25-NH(2) acetylated at positions 156 to 203 [Nop(197), Pya(200), Nle(202)]) and its analogue PL51, in which all methionines were replaced by nonoxidizable Nle. Consistent with a large increase in affinity for BoNT/A, PL50 and PL51 exhibit catalytic efficiencies of 2.6 x 10(6) M(-1) s(-1) and 8.85 x 10(6) M(-1) s(-1), respectively, and behave as the best fluorigenic substrates of BoNT/A reported to date. Under optimized assay conditions, they allow simple quantification of as little as 100 and 60 pg of BoNT/A, respectively, within 2 h with a classical fluorimeter. Calibration of the method against the mouse 50% lethal dose assay unequivocally validates the enzymatic assay.

Clinical comparisons of botulinum neurotoxin formulations

BACKGROUND

The expanding uses of botulinum neurotoxin (BoNT) for a growing number of clinical indications, including cervical and other dystonias, adult and childhood spasticity, and hyperhidrosis, in conjunction with the emergence of new formulations of BoNT, prompt discussion of the differences in formulations, serotypes, and indications for different neurologic diseases.

REVIEW SUMMARY

This review will evaluate evidence from preclinical studies, prospective treatment studies, and direct comparative trials to discuss the differences among BoNTs and the clinical implications of using these different drugs. Data from these sources indicate that formulations of BoNT are distinct; even the same serotype formulations of BoNT serotype A have different molecular structures and sizes and therapeutic indices (reflected in different safety and efficacy profiles).

CONCLUSION

Taken together, these findings confirm that the different BoNT serotypes, including the different BoNTA formulations, are distinct therapeutic entities.

Subcutaneous Botulinum toxin type A reduces capsaicin-induced trigeminal pain and vasomotor reactions in human skin

The present human study aimed at investigating the effect of subcutaneous administration of Botulinum toxin type A (BoNT/A) on capsaicin-induced trigeminal pain, neurogenic inflammation and experimentally induced cutaneous pain modalities. Fourteen healthy males (26.3+/-2.6 years) were included in this double-blind and placebo-controlled trial. The subjects received subcutaneous BoNT/A (22.5U) and isotonic saline in the mirror sides of their forehead. Pain and neurogenic inflammation was induced by four intradermal injections of capsaicin (100mug/muL) (before, and days 1, 3 and 7 after treatments). The capsaicin-induced pain intensity, pain area, the area of secondary hyperalgesia, the area of visible flare and vasomotor reactions were recorded together with cutaneous heat, electrical and pressure pain thresholds. BoNT/A reduced the capsaicin-induced trigeminal pain intensity compared to saline (F=37.9, P<0.001). The perceived pain area was smaller for the BoNT/A-treated side compared to saline (F=7.8, P<0.05). BoNT/A reduced the capsaicin-induced secondary hyperalgesia (F=5.3, P<0.05) and flare area (F=10.3, P<0.01) compared to saline. BoNT/A reduced blood flow (F(1,26)=109.5, P<0.001) and skin temperature (F(1,26)=63.1, P<0.001) at the capsaicin injection sites compared to saline and its suppressive effect was maximal at days 3 and 7 (P<0.05, post hoc test). BoNT/A elevated cutaneous heat pain thresholds (F=17.1, P<0.001) compared to saline; however, no alteration was recorded for electrical or pressure pain thresholds (P>0.05). Findings from the present study suggest that BoNT/A appears to preferentially target Cfibers and probably TRPV1-receptors, block neurotransmitter release and subsequently reduce pain, neurogenic inflammation and cutaneous heat pain threshold.

The Intercostal NMJ Assay: a new alternative to the conventional LD50 assay for the determination of the therapeutic potency of botulinum toxin preparations

Therapeutic botulinum neurotoxin type A preparations have found an increasing number of clinical uses for a large variety of neuromuscular disorders and dermatological conditions. The accurate determination of potency in the clinical application of botulinum toxins is critical to ensuring clinical efficacy and safety, and is currently achieved by using a lethal dose (LD50) assay in mice. Ethical concerns and operational constraints associated with this assay have prompted the development of alternative assay systems that could potentially lead to its replacement. As one such alternative, we describe the development and evaluation of a novel ex vivo assay (the Intercostal Neuromuscular Junction [NMJ] Assay), which uses substantially fewer animals and addresses ethical concerns associated with the LD50 assay. The assay records the decay of force from electrically-stimulated muscle tissue sections in response to the toxin, and thus combines the important mechanisms of receptor binding, translocation, and the enzymatic action of the toxin molecule. Toxin application leads to a time-related and dose-related reduction in contractile force. A regression model describing the relationship between the applied dose and force decay was determined statistically, and was successfully tested as able to correctly predict the potency of an unknown sample. The tissue sections used were found to be highly reproducible, as determined through the innervation pattern and the localisation of NMJs in situ. Furthermore, the efficacy of the assay protocol to successfully deliver the test sample to the cellular target sites, was critically assessed by using molecular tracer molecules.

Production and characterization of monoclonal antibody to botulinum neurotoxin type B light chain by phage display

A monoclonal antibody to the light chain of botulinum neurotoxin type B (BoNT/B) was generated and its protective activity was evaluated in vivo. A chimeric rabbit/human Fab library was generated using bone marrow and spleen cDNAs of rabbits immunized with the BoNT/B light chain, and three monoclonal antibodies specific to the catalytic domain of BoNT/B were isolated. One of these clones, BCXRH1, was specific to a conformation-dependent epitope, and partially neutralized the BoNT/B complex in vivo.

Comparing two botulinum toxin type A formulations using manufacturers? product summaries

BACKGROUND AND OBJECTIVE

Because of the unique pharmacology and clinical versatility of botulinum toxin (BoNT), particularly BoNT serotype A (BoNTA), a need exists for discussion of the current data on similarities and differences between two BoNTA products, BOTOX and Dysport.

METHODS

We compared the physiochemical and pharmacological properties of BOTOX and Dysport using information from the Summary of Product Characteristics (SmPC) documents from a number of countries around the world.

RESULTS AND DISCUSSION

Our analysis based on the SmPC documents demonstrated distinct differences in physical characteristics, breadth of approved indications, dosing and administration, and the incidence and severity of adverse events.

CONCLUSION

BOTOX and Dysport are not bioequivalent. Many of the differences between BOTOX and Dysport discussed within are probably related to the differences in their physical characteristics.

Botulinum neurotoxin type A in facial aesthetics

Injection of botulinum neurotoxin type A has rapidly become the most common non-surgical cosmetic procedure performed, due to its exceptional safety profile, as well as its ability to rejuvenate and enhance a number of facial areas. There are several marketed botulinum neurotoxin preparations, but products are not interchangeable as each possesses distinctive characteristics that are attributed to the unique toxin purification and manufacturing processes. These differences can emerge in the form of potency, duration of effect and the potential for migration outside targeted tissue, causing unwanted effects. However, although there are established preclinical pharmacologic and therapeutic differences between products, there are few well-controlled clinical comparisons in facial aesthetics. It is important for clinicians using these products to understand these differences as they relate to achieving desired outcomes for patients who seek improved facial aesthetics.

Botulinum neurotoxins and formalin-induced pain: central vs. peripheral effects in mice

Neurotoxins affecting neuroexocytosis can represent an innovative pharmacological approach to the investigation of neural mechanisms of pain. Our interest has been focused on the use of botulinum neurotoxins (BoNTs), whose peripheral effects are extensively documented, while the effects on the central nervous system are much less clear. We have investigated both peripheral (sc into the hindpaw) and central (icv) effects of two BoNTs isoforms, BoNT/A and BoNT/B, on inflammatory pain. BoNT/A (sc: 0.937-15; icv: 0.937-3.75 pgtox/mouse) and BoNT/B (sc: 3.75, 7.5; icv: 1.875, 3.75 pgtox/mouse) were injected in CD1 mice and tested in the formalin test 3 days later. Licking response, as index of pain, and behavioral parameters, such as general activity and grooming, were recorded for 40 min during the test. BoNT/A partially affects the licking response in the second phase of formalin test in a similar magnitude of attenuation whether peripherally or centrally administered. BoNT/A does not significantly affect licking behavior during the first phase of the test. Peripheral administration of BoNT/B attenuates the licking response during the first phase not modifying the second phase, while the icv administration has hyperalgesic effect on the interphase of the formalin test. General activity and grooming behavior are not affected either by peripheral or by central administration of BoNTs. Our results show for the first time a central effect of BoNTs that differently modulate inflammatory pain depending both on serotype and on route of administration. Such data suggest BoNTs as a useful tool in the studies aimed at the comprehension of the mechanisms of inflammatory pain.

Adenoviral clostridial light chain gene-based synaptic inhibition through neuronal synaptobrevin elimination

Clostridial neurotoxins have assumed increasing importance in clinical application. The toxin's light chain component (LC) inhibits synaptic transmission by digesting vesicle-docking proteins without directly altering neuronal health. To study the properties of LC gene expression in the nervous system, an adenoviral vector containing the LC of tetanus toxin (AdLC) was constructed. LC expressed in differentiated neuronal PC12 cells was shown to induce time- and concentration-dependent digestion of mouse brain synaptobrevin in vitro as compared to control transgene products. LC gene expression in the rat lumbar spinal cord disrupted hindlimb sensorimotor function in comparison to control vectors as measured by the Basso-Beattie-Bresnahan (BBB) scale (P<0.001) and rotarod assay (P<0.003). Evoked electromyography (EMG) showed increased stimulus threshold and decreased response current amplitude in LC gene-transferred rats. At the peak of functional impairment, neither neuronal TUNEL staining nor reduced motor neuron density could be detected. Spontaneous functional recovery was observed to parallel the cessation of LC gene expression. These results suggest that light chain gene delivery within the nervous system may provide a nondestructive means for focused neural inhibition to treat a variety of disorders related to excessive synaptic activity, and prove useful for the study of neural circuitry.

Primary cell culture for evaluation of botulinum neurotoxin antagonists

The actions of botulinum neurotoxin (BoNT) were studied on evoked release of the neurotransmitter glycine in primary mouse spinal cord cells. 3[H]-glycine was taken up by cells in physiological solution and released by depolarization with 56 mM K+ in the presence of 2 mM Ca2+. Release of 3[H]-glycine was found to be inhibited by BoNT serotypes A, B and E with similar potency ratios to those observed in the acutely isolated mouse diaphragm muscle. When spinal cord cultures were exposed to BoNT/A for 24 h, inhibition of 3[H]-glycine release was detected at toxin concentrations as low as 10(-14) M, and complete inhibition was observed at concentration >or=10(-12) M. Preincubation of BoNT/A with polyclonal equine antiserum led to antagonism of toxin-induced inhibition of 3[H]-glycine release in spinal cord cells and to protection of mice from the lethal effects of BoNT/A. It is concluded that spinal cord neurons are a useful model for studying botulinum intoxication and for evaluating BoNT antagonists.

Complications with the use of botulinum toxin type a in facial rejuvenation: report of 8 cases

The botulinum toxin A is produced by Clostridium botulinum and causes a reversible, selective muscle relaxation that leads to a temporary flattening of the mechanical component of wrinkling without the stigmata of invasive surgery. Since the end of the 1980s, this neurotoxin has been used to treat mimic facial lines with good results. Although this is considered a safe therapy, with adverse effects typically self-limited, more severe complications have been observed when it is used by nonskilled physicians or in improper dosages. This article reports eight patients treated with botulinum toxin A for aesthetic purposes who developed different complications. Treatment of the complication included the use of electrical stimulation, lymphatic drainage, antiinflammatory therapy, dipivefrine cloridrate drops, and other approaches. With specific treatment for each patient, the lengths of these complications seemed to be reduced.

Basic immunological aspects of botulinum toxin therapy

Previous studies in this laboratory had mapped the immune recognition profile of the regions recognized antibodies (Abs) and by T cells on the protective H(C) domain (C-terminal fragment corresponding to residues 855-1296 of the heavy chain) of botulinum neurotoxin serotype A (BoNT/A). The localization of these regions has several potential applications and has provided a basis for the understanding of immunoresistance to treatment. We briefly outline these localized regions and discuss the impact of these findings on the immunotherapeutic applications of BoNT/A. Immunoresistance to toxin therapy can appear in some patients after a few injections with the toxin. Our epitope mapping studies have shown that several factors can influence the immune response to the toxin. These factors include dose, duration of treatment, frequency of immunization, and quality of the toxin. The immune response to the whole toxin is under genetic control, and the response to each epitope is under separate genetic control. Therefore, the appearance of blocking Abs (i.e., immunoresistance) in patients might be controlled by the major histocompatability of the host. Once a patient becomes immunoresistant to one toxin then switching to another toxin will most often be of limited and short-lived benefit, because the patient becomes rapidly immunoresistant to the second toxin. Finally, because of the considerable structural homology between tetanus neurotoxin (TeNT) and BoNTs, it is possible, although not certain, that a prior active immune response to TeNT might play some role in the early appearance on anti-BoNT Abs in some patients.

Detection of antibodies against botulinum toxins

After immunisation with botulinum vaccine, antibodies to multiple epitopes are produced. Only some of these will have the capacity to neutralise the toxin activity. In fact, the ability of toxoid vaccine to induce toxin neutralising antibodies has provided the basis for the use of therapeutic antitoxins and immunoglobulins for the prophylaxis and treatment of diseases caused by bacterial toxins. Increasing indications for the chronic use of botulinum toxin for therapy have inevitably resulted in concern for patients becoming unresponsive because of the presence of circulating toxin-specific antibodies. Highly sensitive and relevant assays to detect only clinically relevant toxin neutralising antibodies are essential. Although immunoassays often provide the sensitivity, their relevance and specificity is often questioned. The mouse protection LD(50) bioassay is considered most relevant but can often only detect 10 mIU/ml of antitoxin. This sensitivity, although sufficient for confirming protective immunity, is inadequate for patients undergoing toxin therapy. An intramuscular paralysis assay improves the sensitivity to ca. 1 mIU/ml, and a mouse ex vivo diaphragm assay, with sensitivity of < 0.5 mIU/ml, is the most sensitive functional assay to date for this purpose. Alternative approaches for the detection of antibodies to botulinum toxin have included in vitro endopeptidase activity neutralisation. Unlike any other functional assay, this approach is not reliant on serotype-specific antibodies for specificity. Most recent promising developments are focused on cellular assays utilising primary rat embryonic cord cells or more conveniently in vitro differentiated established cell lines such as human neuroblastoma cells.

Growing Old Disgracefully: The Cosmetic Use of Botulinum Toxin

The explosive growth in the use of botulinum toxin for cosmetic purposes has undoubtedly had an impact on the number of animals used in the potency testing of this product. The test used is a classical LD50, a severe procedure during which animals experience increasing paralysis until the occurrence of death. The enthusiastic adoption by the general public of the use of botulinum toxin as an anti-wrinkle treatment has, at least in Europe, paradoxically taken place against a background of moves to stop animal testing of cosmetics and cosmetic ingredients. There appears to be a dearth of information aimed at the public concerning botulinum toxin testing. Botulinum toxin does have important medical applications; however, the question arises whether a blanket licence for the testing can be justified, when a large proportion of the product is being used cosmetically. A further question is why death continues to be the endpoint of the potency test, when a more-humane endpoint has been proposed. In addition, a number of alternative methods have been developed, which could have the potential to replace the lethal potency test altogether. These methods are discussed in this paper, and the importance of establishing a strategy for their validation is emphasised, a need that has become even more urgent in the light of the recently published draft monograph on botulinum toxin by the European Pharmacopoeia Commission.

Quality-of-life assessment in patients with hyperhidrosis before and after treatment with botulinum toxin: results of an open-label study

BACKGROUND

Patients with hyperhidrosis, a disorder characterized by increased sweat production, experience substantial functional and emotional problems. Botulinum toxin type A (BTX-A) has been shown to be useful in the treatment of hyperhidrosis; however, few studies have considered the effects of treatment on patients' quality of life (QOL).

OBJECTIVES

The objectives of this study were to assess QOL in patients with focal hyperhidrosis; to investigate whether the impairment in QOL in these patients is related to the type of hyperhidrosis or the number of sites involved; and to compare the changes in QOL and the response to BTX-A treatment in patients with axillary and palmar hyperhidrosis.

METHODS

Patients with focal primary hyperhidrosis of the axillae, palms, and soles who had experienced decreased QOL and whose condition had not responded to conventional topical and physical therapies were included in this open-label study. Patients completed a self-administered Dermatology Life Quality Index (DLQI) questionnaire before and 2 weeks after treatment with BTX-A.

RESULTS

All 41 patients had experienced a decrease in QOL as measured by the DLQI. The impairement in QOL was not dependent on the number or types of sites involved. Treatment with BTX-A led to improvement in QOL in all patients, with the median DLQI score decreasing (ie, improving) significantly from pretreatment level (P < 0.001). The improvement in QOL and response to treatment were similar in patients with axillary and palmar hyperhidrosis.

CONCLUSIONS

Further studies with a longer follow-up period are needed to assess the long-term effects of BTX-A; however, preliminary data from the present study suggest that BTX-A improves QOL in patients with focal hyperhidrosis, independent of the presenting clinical picture.

Cross reaction of tetanus and botulinum neurotoxins A and B and the boosting effect of botulinum neurotoxins A and B on a primary anti-tetanus antibody response

The present studies were carried out in order to investigate the cross-reaction of botulinum neurotoxins (BoNTs) with human and mouse antibodies against tetanus neurotoxin (TeNT) and determine whether injection of BoNT into a host that has been primed with TeNT would result in boosting of the response to the injected BoNT. Human antisera against TeNT obtained from 9 individuals were found to exhibit substantial cross-reaction with BoNTs A and B. We prepared antibodies (Abs) against inactivated tetanus neurotoxin (TeNT) in outbred mice and determined the binding of these Abs to active TeNT and active botulinum neurotoxins (BoNTs) A and B. Blood samples were collected before immunization (day 0) and on days 42, 82 and 125 after the first injection. The reactions of these sera with the immunizing antigen (inactivated TeNT), active TeNT, active BoNT/A and active BoNT/B were determined. At a fixed dilution (1:62.5 v/v), the sera contained high levels of Abs that reacted with TeNT and also with BoNTs A and B. Throughout the test period (up through day 125) and at different dilutions the cross-reactions of the antisera with BoNT/B were almost twice those with BoNT/A. The reactions of the antisera with the immunizing antigen (inactive TeNT) or with active TeNT were essentially equal throughout the dilution range tested (1:16-1:500 v/v). To determine whether injection of BoNT/A or B into a host that had been primed with TeNT resulted in boosting of the response to the priming antigen (TeNT) as well as BoNT/A or B, mice were primed with TeNT and boosted 21 days later with TeNT, BoNT/A or BoNT/B. Appropriate controls were also employed. Blood samples were collected prior to TeNT priming (day -1) and on days 21, 32, 46 and 67 after priming. In TeNT-primed mice, BoNTs A or B boosted the anti-TeNT Ab responses slightly but had no significant boosting effect on the Ab populations that bind to BoNTs A or B. It is concluded that while Abs against TeNT cross react with BoNTs and the cross reaction with BoNT/B is almost double that of BoNT/A, injection of BoNTs A or B in the presence of a prior active immunity against TeNT is not very likely to make the host mount an Ab response against the injected BoNT.

Anomalous enhancement of botulinum toxin type A neurotoxicity in the presence of antitoxin

The neutralization of botulinum toxin serotype A with polyclonal equine antitoxin was studied in isolated mouse hemidiaphragms and compared to the same action in live mice. The biological activity of the toxin in the isolated muscle could be markedly reduced with excess antitoxin, estimated as 3:1 molar ratios of IgG Ab:toxin or better. Toxin neutralization in vivo required higher ratios of Ab:toxin, ranging from 30:1 at high toxin doses and increasing to 100:1 at 10xLD50 toxin. At equimolar Ab to toxin ratios in the isolated muscle, the biological activity of the toxin underwent a statistically significant increase. This paradoxical effect of the polyclonal antisera was serotype selective and independent of the presence or absence of hemagglutinin in the toxin. The enhancement of toxin activity was subsequently localized to occupancy of one of four epitopes on the toxin using monoclonal antibodies to mimic the effect of the antitoxin. The enhancement of toxin activity suggests that botulinum toxin may undergo a conformational change upon binding antibodies to certain domains. This phenomenon could contribute to the observed concentration dependent changes in neutralization efficacy with antitoxin in vivo.

Pharmacology of botulinum toxin

BACKGROUND

Botulinum toxin has a well-defined role among dermatologists for the treatment of facial wrinkling, brow position, and palmar and axillary hyperhidrosis.

OBJECTIVE

The purpose of this study is to educate dermatologists on the pharmacology of botulinum toxin.

METHODS

A retrospective review of the literature on botulinum toxin from 1962 to the present was conducted. We examined the clinical applications of botulinum toxin, cholinergic neuromuscular transmission, the toxin's structure and molecular actions, drug and disease interactions at the neuromuscular junction, toxin assays, determinants of clinical response, and adverse side effects.

RESULTS

Botulinum toxin blocks the release of acetylcholine from the presynaptic terminal of the neuromuscular junction. Several drugs and diseases interfere with the neuromuscular junction and the effects of botulinum toxin. The mouse bioassay, the most sensitive and specific measurement of toxin activity, is the gold standard for botulinum toxin detection and standardization. The major determinants of clinical response to treatment are the toxin preparation, individual patient's anatomy, dose and response relationships, length of toxin storage after reconstitution, and immunogenicity. To minimize potential antibody resistance, one should use the smallest effective dose, utilize treatment intervals of more than 3 months, and avoid booster injections. Uncommon adverse effects include ptosis, ectropion, diplopia, bruising, eyelid drooping, hematoma formation, and temporary headaches.

CONCLUSION

Botulinum toxin is a safe and effective treatment. Knowledge of the pharmacologic basis of therapy will be useful for standardizing techniques and achieving consistent therapeutic results in the future.

Palmar and axillary hyperhidrosis treated with botulinum toxin: one-year clinical follow-up

Focal hyperhidrosis is a common and sometimes handicapping condition for which the presently most effective treatment, sympathectomy, often leads to irreversible side-effects. We aimed to study effectiveness and tolerability of an alternative treatment with botulinum toxin injections over a period of one year for this condition. Twenty-eight patients with palmar (n = 19) and/or axillary (n = 13) hyperhidrosis were treated with intracutaneous injections of botulinum toxin (Botox(R)) 2 U/4 cm2. Sweat function was studied clinically and by objective measurements after treatment of one side. Treated and untreated sides, and pre- and post-treatment skin areas were compared. Subjective evaluation was performed after treatment of one side and 2-5 months after treatment of both sides. Duration of effect was controlled by a one-year follow-up. Sweating disappeared in eight out of 13 patients with axillary and in five out of 19 with palmar hyperhidrosis, and was reduced markedly in another five out of 13 and 10 out of 19 patients. Two-thirds of those treated for hand sweat noticed a slight and transient reduction of power of finger grip. No side-effects were noticed after treatment of axillary hyperhidrosis. We find intracutaneous injections of botulinum toxin with this technique safe and effective, and due to the relatively long duration of effect the treatment should be recommended before sympathectomy for focal hyperhidrosis.

DNA vaccination using the fragment C of botulinum neurotoxin type A provided protective immunity in mice

Botulinum neurotoxin (BoNT) is one of the most toxic substances known to produce severe neuromuscular paralysis. The currently used vaccine is prepared mainly from biohazardous toxins. Thus, we studied an alternative method and demonstrated that DNA immunization provided sufficient protection against botulism in a murine model. A plasmid of pBoNT/A-Hc, which encodes the fragment C gene of type A botulinum neurotoxin, was constructed and fused with an Igkappa leader sequence under the control of a human cytomegalovirus promoter. After 10 cycles of DNA inoculation with this plasmid, mice survived lethal doses of type A botulinum neurotoxin challenges. Immunized mice also elicited cross-protection to the challenges of type E botulinum neurotoxin. This is the first study demonstrating the potential use of DNA vaccination for botulinum neurotoxins.

Glial cells promote muscle reinnervation by responding to activity-dependent postsynaptic signals

After nerve injury, denervated synaptic sites in skeletal muscle commonly become reinnervated by sprouts that grow from nerve terminals on nearby muscle fibers. These terminal sprouts grow along a glial cell guide or "bridge" formed by Schwann cell (SC) processes that extend from denervated synaptic sites. Data presented here show that most bridges connect innervated and denervated synaptic sites rather than pairs of denervated sites even when most sites in the muscle are denervated. Furthermore, bridges are inhibited by presynaptic or postsynaptic blockade of synaptic transmission, manipulations that do not alter the extent of SC growth. These results show that an activity-dependent postsynaptic signal promotes the formation and/or maintenance of glial bridges and thus muscle reinnervation.

Synaptophysin is phosphorylated in rat cortical synaptosomes treated with botulinum toxin A

Phosphorylation and dephosphorylation of neuronal proteins have been implicated in regulation of synaptic transmission. Studies were performed to determine if synaptophysin was phosphorylated or dephosphorylated during exposure of synaptosomes to botulinum toxin A (BoTX/A). Cholinergic-enriched synaptosomes were preincubated in the presence of 3H-choline to label newly synthesized acetylcholine (3H-ACh). This was followed by incubation with low or high potassium to stimulate release of newly synthesized 3H-ACh. BoTX/A inhibited total Ach release by 15-19% and inhibited release of newly synthesized 3H-ACh by 35%. A 165% increase in synaptophysin phosphorylation occurred in a dose-dependent manner over a range of doses (0.2 nM, 2 nM, 20 nM, 100 nM) of BoTX/A. When 4-Aminopyridine was added to synaptosomes that were BoTX/A treated, synaptophysin was dephosphorylated to control levels. Synaptosomes incubated with BoTX/A exhibited an inhibition of potassium stimulated ACh release and an increase in synaptophysin phosphorylation. Synaptophysin phosphorylation may be involved in inhibition of acetylcholine release.